The invention relates to a photosensitive member for electrophotography, and more particularly, to a photosensitive member including a conductive support, a photoconductive layer and a transparent insulating layer which are sequentially laminated one over another.
A photosensitive member for electrophotography including a conductive support, a photoconductive layer and a transparent insulating layer which are laminated one over another is already known, and is extensively used in electrophotographic copying machines. A variety of techniques are available to form an electrostatic latent image on such member. In one technique, an electrostatic latent image is formed through a series of sequential steps of primary corona charging and concurrent imagewise exposure, secondary corona charging and a flush irradiation, the latent image formed being of the opposite polarity from that of the primary corona charging.
However, when such technique is employed to form a latent image on the surface of a photosensitive member, a difference in the surface potential between a bright and a dark area of the resulting latent image or a contrast voltage is less than a theoretical value, causing the likelihood that an image having a sufficient optical density may not be obtained when the latent image is developed. It is considered that one of the causes for such difficulty would be a migration of a carrier between the conductive support and the photoconductive layer in darkness when such migration should not occur. An attenuation of charge on the photoconductive layer in darkness would be another reason.
To elucidate a mechanism which causes such migration of carrier, a study has been made by the present inventors of the surface configuration of the conductive support, paying attention to the boundary surface between the conductive support and the photoconductive layer which has been put out of consideration heretofore. It is found that the surface of the conductive support of a photoconductive member which exhibited a poor contrast voltage exhibits a significant amount of unevenness and that there is a relationship between such unevenness and the magnitude of the contrast voltage.